This invention relates to novel strains of bacteria which have the ability to control Pythium spp. on small grains under field conditions and a method for the selection of these strains.
The soilborne pathogen complex of Pythium spp. comprises a group of fungi that are among the most successful of all microbial colonists in agricultural soils. It is estimated that nearly all cultivated soil in the world contains spores of at least one, two, three, and even as high as ten Pythium species. The normal nutritional substrate of this pathogen complex are roots of agricultural crops and it is known to cause serious damage to small grain crops such as wheat, oats, barley, rye, and triticale. Such damage includes seed decay, preemergence seedling blight, damage to fine rootlets and root hairs, reduced root length, plant stunting, reduced tillering, uneven height, delayed maturity, and reduced yield. At least ten species of Pythium are known to adversely effect wheat production in the Pacific Northwest (Washington, Oregon, and Idaho), and it has been estimated that Pythium damage causes reduction in wheat yields in this area of 10 to 25 percent, resulting in significant economic losses. This problem may worsen as growers move to minimum and no-till practices. Although exact losses of small grain crops due to Pythium on a worldwide basis are not known, Pythium root rot is considered a serious root disease which causes significant reduction in crop yields.
Presently, the only completely effective method to control Pythium spp. is by soil fumigation using fungicides such as Telone C (1,3-dichloropropene plus 15-17% chloropicrin) or CP 440 (chloropicrin at the rate of 440 kg/ha). While this method is useful in research plots, it is prohibitively expensive for use as a commercial control method.
The fungicide metalaxyl [N-(2,6-dimethylphenyl)-N-(methoxyacetyl)alanine methyl ether] is currently registered for control of Pythium spp.; however this treatment has only limited usefulness because some of the naturally occurring Pythium strains are tolerant to this fungicide. Additionally, for a fungicide to be effective against Pythium, it must be absorbed by the plant and translocated downward systemically in the plant; presently all systemic fungicides available commercially for Pythium control move only in an upward direction in the plant and thus are only minimally effective. Currently, no Pythium resistant varieties of small grains are known.
While use of antagonistic microorganisms as seed or soil treatments for biological control of some root or seedling pathogens has been reported for a variety of plants, no bacterial strain has been previously found which would control Pythium spp. on small grain crops; additionally, no procedure for the selection of bacteria which suppress Pythium in small grains has been reported. Because the physiological characteristics required for a bacterial strain to control disease are very specific as to (1) the disease which is to be controlled; (2) the plant which is effected; (3) the mode of action of the disease control; (4) the activity of the microorganism; (5) the ecological niche of the pathogen and control organism; (6) cultural practices favorable to the disease, and (7) soil and climatic conditions favorable to disease, information about biological treatments for control of other fungal diseases on small grains or control species of Pythium on other plants cannot be used to predict strains of microorganisms which would control Pythium spp. on small grains under field conditions or predict criteria for selecting such strains.